1. Field Of The Invention
The present invention relates generally to the treatment of icy road surfaces with sand and, more particularly, is concerned with a method and apparatus for spreading sand heated sufficiently to cause formation of a "sand paper" road surface.
2. Description Of The Prior Art
It is standard practice in many regions of the United States to treat icy road surfaces by spreading salt crystals from a moving vehicle. The salt crystals react with ice and snow to form a solution having a freezing point which is lower than that of water alone. As a result, the ice melts and the hazardous driving conditions are alleviated. However, the use of salt crystals has many important disadvantages. First, salt does not react with ice at temperatures below 18 degrees Fahrenheit. Second, salt is very destructive of highways and bridges in that it causes deterioration of concrete. Third, the bodies of automobiles experience high degrees of corrosion and rusting in areas of the country where salt is commonly use on the highways. Finally, considerable damage to cropland and pollution of ground water results from runoff of salt-laden water from highways and streets into streams and storm sewers.
In view of the negative aspects of salt, in parts of the country where sand or grit or the like are plentiful they are often substituted for salt. Many different sand distributing devices and mechanisms are known in the prior art. Exemplary devices for providing sand or grit for distribution on icy roads are disclosed by a U.S. patent to McLean (3,399,917) and a Canadian patent to Micheletz (616,582). McLean discloses a pair of sand containers mounted on the frame of a truck for dispensing sand, via an auger, through a discharge tube ahead of the truck wheels. The discharge tube connects the exhaust of the truck to the containers for heating the sand to prevent it from freezing in the containers. Micheletz is similarly directed to an apparatus for applying sand in front of the wheels of a vehicle. The sand boxes are connected to the tail pipe to keep the sand dry and prevent it from freezing. Also, a U.S. patent to Storberg (2,539,197) is directed to the same type of apparatus; however, no heat is applied to the sand. Another U.S. patent to Ten Broeck et al. (4,162,766) shows a conventional apparatus for spreading materials on icy roads which includes a hopper, unloading conveyor and a spreader mechanism. To this conventional apparatus is added an auxiliary hopper for mixing and discharging a second material, such as salt, with the first material (which is cinders). Alternatively, material from the auxiliary tank can be discharged by an auger onto a spreader.
Other U.S. patents to Tift (3,235,107), Arnold (2,060,652) and Tobias (3,768,737) merely disclose devices which distribute sand per se, such as by the use of an auger conveyor to deliver sand to a rotary spreader. Two other U.S. patents to Gray (1,165,331) and Caye (4,022,386) are representative of other spreader devices found in the prior art.
While many of the devices in the above-cited representative prior art patents undoubtedly operated satisfactorily and achieved their objectives under a narrow range of operating conditions for which they were designed, It is not seen that any of these devices propose to handle sand and like materials in a way which extends or enhances the utility of sand as a more or less universal substitute for salt in the treatment of icy road conditions. Consequently, a need exists for further improvements in sand spreading techniques which will more effectively utilize sand as an common remedy for hazardous icy roads.